The present invention relates to a coplanarity measuring apparatus for measuring the coplanarity of the leads of a surface-mount type IC package (to be referred to as an SMD hereinafter).
An apparatus similar to a coplanarity measuring apparatus of this type has been proposed. In such an apparatus, as shown in FIG. 11A, a light source 6 and a semitranslucent diffusion resin 7 are used to radiate light from the inside of an SMD 8 mounted on a flat stage 5. A transmission image, of lead end portions, obtained by the radiation is photographed by a camera 4 to obtain a binary image 29. A distance 31a (float amount) between a dark point group representing each lead and a dark line 31 is calculated by using the binary image 29. The maximum value is then retrieved from all the calculation results. A coplanarity is obtained by multiplying the maximum value by the resolution of the camera 4.
In a coplanarity measuring apparatus of this type, a high-magnification macro lens 30 is used for the camera 4 to realize a camera system resolution of 10 .mu.m/pixel (in the vertical and horizontal directions). For this reason, when the SMD 8 having a lead width of 0.8 mm and a lead pitch of 0.65 mm is to be measured, three or four pins are photographed within the field of view in each framing. Therefore, image processing and coplanarity calculation have been performed by the following three schemes: arranging a plurality of cameras 4 along one side of the SMD 8 (reference numeral 32 in FIG. 11B); shifting the camera 4 in a direction parallel to a side of the SMD 8 by using a stepping motor or a servo motor (reference numeral 33 in FIG. 11B); and moving the flat stage 5 in a direction parallel to the camera 4 while the SMD 8 is mounted on the stage 5 (reference numeral 34 in FIG. 11B).
Referring to FIG. 11A, in the coplanarity measuring apparatus, since the camera 4 is equipped with the high-magnification macro lens 30 to realize a precision of 10 .mu.m/pixel in the vertical direction, the horizontal resolution also becomes 10 .mu.m/pixel, i.e., the field of view is undesirably reduced. For this reason, in order to obtain the float amounts of all leads, a plurality of cameras 4 must be installed along one side of the SMD 8 (reference numeral 32 in FIG. 11B), or the camera 4 must be shifted (reference numeral 33 in FIG. 11B), or the flat stage 5 must be shifted (reference numeral 34 in FIG. 11B).
In the coplanarity measuring apparatus denoted by reference numeral 32 in FIG. 11B, the number of cameras 4 must be increased with an increase in mold size of the SMD 8. In addition, with an increase in number of cameras 4, the numbers of camera controllers, camera drivers, and memories are increased, resulting in an increase in the cost of equipment.
In the coplanarity measuring apparatuses denoted by reference numerals 33 and 34 in FIG. 11B, since image processing and coplanarity calculation are performed while the camera 4 or the flat stage 5 are shifted, vibrations of an operating portion deteriorate the measurement precision. In addition, since the number of shift steps is increased with an increase in the mold size of the SMD 8, the measurement time is undesirably prolonged.